A rule of thumb provides a decision-making framework that covers a far wider range of circumstances.

“This valve here measures the pressure level in the nuclear reactor.

"When the dial exceeds 80%, this red light over here will blink.

"We never want the reactor to exceed 100% of maximum because if it does, we die.

"This green button injects extra coolant into the reactor and keeps all of us from dying.

"If you push the green button when there is no overheating of the reactor, there is no permanent damage.

"We simply have to pay for extra coolant to replenish our supply.”

(Forgive my complete over simplification of a nuclear reactor.)

Assuming everything goes as expected IF the reactor overheats, the dial will indicate so, and the red warning light will go off.

In this ideal scenario (relatively speaking), both the person who follows the rule and the person who follows the rule of thumb can achieve the desired outcome.

The problem with ideal scenarios is they don’t always occur as often as we would like.

For example, let's say the dial shows 101% and is increasing, but the red light doesn’t actually go on.

What would each type of employee do under the circumstances?

In the case of the “rule” follower, she does nothing. The rule was very clear.

The dial must exceed, AND the red light must turn on.

Given only one of the two triggering conditions was satisfied, the rule says to do nothing. She and everyone else dies as a result.

In the case of the “rule of thumb” follower, she understands the purpose of the various gauges and warning lights.

She also understands the function of the green button and her role in the overall safety system.

Even if the warning light doesn’t go on, the dial clearly shows an imminent catastrophic death situation.

The "rule of thumb” follower will likely push the green button. She’ll do so because she understands the information being conveyed by the dial.

She also understands her role in the process, the function of the button, and the consequences of pushing the button across a wide range of scenarios.

If the dial is accurate, she will have saved everyone’s life, including her own.

If the dial isn’t accurate, she will have erred on the side of caution, caused no permanent damage, and have the company incur a slightly higher materials cost — a small price to pay to avoid complete catastrophe.

Now in everyday life, most of us aren’t faced with life and death decisions. However, nearly every task or area of responsibility can be defined as a set of "rules" or "rules of thumb.”

In general, the simpler the task at hand, the more likely a set of explicit “rules” will cover all likely scenarios.

The more complicated the task, the more likely that “rules” will leave certain conditions unaddressed.

In these situations, “rules of thumb” work a whole lot better for everyone involved.

The problem is that cases have an infinite number of variations. It’s impossible to create a rule for every nuance, subtlety, and variation of a case.

From a consulting firm’s point of view, the entire case interview process is designed to find new hires that can follow "rules of thumb," as opposed to blindly following “rules” when they clearly don’t apply.

The difference between an individual contributor and a department head is in part attributed to the department head’s ability to follow “rules of thumb” across a wide range of not always predictable situations.

Here’s a simple way to expand your skills in this area.

Anytime someone gives you a rule, but doesn’t explain WHY the rule exists, you must pause.

Ask them the purpose, function, and roles of the various steps and actors the rule is designed to cover.

Don’t blindly do what you’re told.

Ask WHY.

Managers and leaders sometimes forget to explain the details.

(I know I do this a lot. I have several dozen tasks, projects, and ideas in my head at once. I often forget who I’ve explained things to before and who I haven’t. I rely on my staff to tell me when they don’t understand something.)

If you’re a manager aspiring to be a leader, it is worth investing in teaching your team to be “rule of thumb” followers rather than merely “rule” followers.

It requires extra work up front. “Rule" followers don’t need any background knowledge, but “rule of thumb” followers do.

This requires either some effort to teach them this information individually or to develop a reusable training system that provides this background knowledge to new members of your team.

The more your team can effectively follow “rules of thumb,” the more you can delegate bigger, more complicated, and less well-defined projects.

When your team can’t follow “rules of thumb,” what ends up happening is they go to you to make a decision because a real life situation came up that didn’t fit any of the pre-defined rules.

This is why many leaders (especially in smaller businesses) get decision fatigue.

At some point, your brain gets saturated.

You can’t possibly absorb all the millions of small details surrounding every single micro decision that needs to be made every day.

It’s actually easier to transfer to others the ability to make decisions using “rules of thumb” without you ever hearing about the million details.

The exception is when the stakes or consequences involved in a decision exceed a certain threshold, you can set a rule to involve you.

(Incidentally, one of the reasons many people like my teaching style is because I almost always teach “rules of thumb” even if asked to teach a “rule.”

A “rule” is useful in the moment. A “rule of thumb” can often be useful for life.)

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Thank you for such a great article. As always I enjoy reading your writings.

I would like to point out that using the word “rule of thumb” is politically risky as it drives from an original ruling done in 1782 by Judge Sir Francis Buller (English Law) who ruled that a man is allowed to beat his wife with a stick that is no thicker than his thumb.

I recall learning this when I was doing my MBA at McGill University, my accounting teacher was very serious about not using this expression, and we would get penalized heavily if someone used it in the assignments.

I fully understand that many people use the expression to express a broadly accurate guide or principle, based on experience or practice rather than theory (online dictionary is helping me in here).

What do you think of the idea of brain storming about replacing this expression by a new expression?